Railway car brake mechanism

ABSTRACT

Railway brake device having brake discs rigid with car wheels, and brake means in the form of toggle joint mechanisms with rods movable into alignment for braking actions against these discs by the relative movement of air pressure cylinder and piston devices having articulated connections between adjoining ends of such rods and the piston rod. A spring in this cylinder acts progressively to decrease the input force exerted on the toggle to the extent that the resultant output braking force resulting from the progressively increasing mechanical advantage of the toggle acting on said progressively decreasing input force, is substantially uniform over a major portion of the brake applying movement of the cylinder and piston mechanism.

United States Patent Inventor Edward G. Goods Snyder, N.Y. Appl. No. 15,628 Filed Mar. 2, 1970 Patented Sept. 14, 1971 Assignee Buffalo Brake Beam Company Continuation-impart of application Ser. No. 727,781 May 9, 1968, now abandoned which is a continuation of application Ser. No. 61 1,860, Jan. 26, 1967, now Patent No. 3,422,131, which is a continuation-in-part of application Ser. No. 417,658, Dec. 11,

1964, now Patent No. 3,307,659.

RAILWAY CAR BRAKE MECHANISM 8 Claims, 23 Drawing Figs.

US. Cl 188/59, 188/ 153 Int. Cl Fl6d 55/32 Field of Search 188/58, 59,

[5 6] References Cited UNITED STATES PATENTS 3,307,659 3/1967 Goods 188/59 Primary Examiner-Duane A. Rege r Att0rneyMorrison, Kennedy & Campbell ABSTRACT: Railway brake device having brake discs rigid with car wheels, and brake means in the form of toggle joint mechanisms with rods movable into alignment for braking actions against these discs by the relative movement of air pressure cylinder and piston devices having articulated connections between adjoining ends of such rods and the piston rod. A spring in this cylinder acts progressively to decrease the input force exerted on the toggle to the extent that the resultant output braking force resulting from the progressively increasing mechanical advantage of the toggle acting on said progressively decreasing input force, is substantially uniform over a major portion of the brake applying movement of the cylinder and piston mechanism.

PATENTED SEP 1' 4 I971 SHEET 3 OF 8 INVENTOR f 01149190 6 qaaas PATENTED SEPI 4 I971 SHEET 8 0F 8 INVENTOR. /mo 6% 6000s ATTO NEY \Q g Q RAILWAY CAR BRAKE MECHANISM The present invention relates to railway car brake mechanisms, especially of the freight type, and is an improvement upon the inventions shown and described in Busch U. S. Pat. No. 2,903,096, 2,903,097 and 2,903,098. The present application is a continuation-in-part of application Ser. No.

727,787 filed May 9, 1968, now abandoned which is a true continuation of application Ser. No. 611,860, filed Jan. 26, 1967, (now Pat. No. 3,422,131 which in turn is a continuation-in-part of application Ser. No. 417,658, filed Dec. 11, 1964 (now US. Pat. No. 3,307,659).

In the application of railway brakes by power derived from air under pressure, a single air storage reservoir is usually employed for each railway car for the operation of the brakes on the two tucks of the car. As the air under pressure is discharged from the reservoir during the application of the brakes, the pressure progressively decreases due to the expansion of the air. It is important that steps be taken to compensate for this decrease in air pressure to assure that the braking force applied is effective.

A toggle joint mechanism is highly desirable for the application of railway brakes because it has the characteristic of progressively increasing its mechanical advantage, as the articulated arms of the mechanism move towards alignment. However, the rate of increase of mechanical advantage of the toggle joint mechanism is high, especially towards the terminal phase of its braking stroke, so that the decrease in the rate of air pressure used to actuate such a mechanism would be overcompensated by this mechanism. As a result, the sudden increase of braking power applied by the airpowered toggle joint mechanism during the terminal phases of the braking stroke of themechanism, is excessively shocking to the railway car and the other cars of the train. 7

One object of the present invention is to provide new and improved airpowered toggle joint means, which apply the brakes to a railway car, and which avoid the disadvantages described.

To attain the objective described, each toggle joint mechanism is actuated by a fluid-operated unit, comprising an air cylinder and piston device into which air under pressure from the main pressure air reservoir of the car is delivered upon application of the brakes. Acting against the force transmitted to the toggle joint mechanism by the air acting on the piston in said air cylinder is a coil spring. This coil spring is progressively compressed during the braking stroke, and reduces progressively thereby, the force transmitted to the toggle brake mechanism during its braking stroke. The resultant force transmitted by the toggle joint mechanism during its braking stroke will be leveled off by the progressively counteracting effect of the coil spring, so that the braking force transmitted by the toggle joint mechanism to the brake shoes is substantially more uniform during the piston stroke than would be the case in the absence of such a coil spring.

As a further feature, the coil spring also serves to return the toggle joint mechanism and its associated movable parts into inoperative position away from braking position upon releases of the brakes, so that the brake shoes are moved away from the braking surfaces of the brake system.

Another object of the present invention is to provide a railway brake system with toggle joint mechanisms designed to apply substantially constant braking pressures, regardless of wear on the brake shoes.

A further object of the present invention is to provide a new and improved hand-operated transmission system, employable as an alternative to a fluid-operated force-applying system, for operating the toggle joint mechanism of a railway brake system.

Various other objects, features and advantages of the present invention are apparent from the following description and from an inspection of the accompanying drawings, in which FIG. 1 is a top plan view of a railway car truck having a braking system constituting an embodiment of the present invention;

FIG. 2 is a top plan view of part of the railway car truck shown in FIG. 1, but on a larger scale;

FIG. 2a is a perspective of the end of an equalizer bar forming part of the'support structure for the braking system;

FIG. 3 is a section of the railway car truck taken on lines 3- 3 of FIG. 2;

FIG. 4 is a detail section of the brake system taken on lines 4-4 of FIG. 2;

FIG. 5 is a detail section of the brake system taken on lines 5-5 of FIG. 2;

FIG. 6 is a detail section of the railway car truck taken on lines 6-6 of FIG. 1;

FIG. 7 is a detail section of the railway car truck taken on lines 7-7 of FIG. 6;

FIG. 8 is a detail section of the brake system taken approximately on lines 8-8 of FIG. 4;

FIG. 9 is a top plan view of part of one of the equalizer bars forming part of the support structure for the braking system;

FIG. 10 is a top plan view of part of the other equalizer bar forming part of the support structure for the braking system;

FIG. 1 l is the end view of the equalizer bar shown in FIG. 9;

FIG. 12 is an end view of the other equalizer bar shown in FIG. 10;

FIG. 13 is a detail section taken on lines 13-13 of FIG. 9;

FIG. 14 is a detail section taken on lines l4 14 of FIG. 12;

FIG. 15 is a view partly in side elevation and partly in section of the fluid-operated unit operable to actuate one of the toggle joint mechanisms of the brake system, the view being taken approximately along the lines l5-l5 of FIG. 16;

FIG. 16 is a partial end view of the fluid-operated unit shown in FIG. 15;

FIG. 17 is a graph showing the force in the air brake cylinder due to air pressure for different travels of the piston operating the toggle joint mechanism;

FIG. 18 is a graph showing the braking force on a brake disc by a toggle mechanism operating without a return spring for different travels of the piston operating said mechanism;

FIG. 19 is a graph showing the force delivered by the piston resisted by a return spring and operating the toggle joint mechanism, said force being shown for different travels of said piston;

FIG. 20 is a graph showing the braking force on the brake disc due to the force delivered by the toggle joint mechanism operating with a return spring;

FIG. 21 is a view in vertical section of a different fluid operating unit for actuating a toggle joint mechanism of the brake system, the view being taken approximately along the line 21-21 of FIG. 22; and

FIG. 22 is a partial end view of the fluid-operated unit shown in FIG. 21.

Referring to FIGS. 1-3 of the drawings, there is shown a railway freight car truck comprising a pair of side structures or frames 10 having respective guide openings 11 to receive the ends of a conventional truck bolster 12 extending between said frames and projecting at the ends into said openings, where they are supported on coil springs (not shown) and are guided by side columns 13 of said openings for vertical shockabsorbed movement. The bolster 12 is provided at its ends with lugs 14 engaging the inboard sides of the side columns 13 of the side frames 10 and lugs (not shown) engaging the outboard side of the side columns. These lugs 14 guide the bolster 12 for vertical movement.

The bolster 12 is also provided with a center conformation 16 for direct pivotal connection to the underside of the railway car body in a conventional manner. Between the two side frames 10 and supported thereon by suitable bearings are two parallel axles 17 carrying on opposite ends, flanged car wheels 18 which ride on rails 19.

To support certain operating parts of the brake mechanism and at the same time to sustain the side frames 10 against the stresses of the braking action, there are provided two equalizer bars.20 and-20a (FIGS. 1-14) on opposite sides of the bolster 12, each bar being pivotally connected at its ends by means of hinge pins 21 to brackets 22 integral or otherwise fixedly secured to the side frames.

The side frames are shown of the conventional type employed with brake mechanisms having brake beams with their ends slidable in guides on the inboard sides of said side frames. In the specific shown, these brake beam guides are defined by the brackets 22, and since these guides usually slant downwardly towards each other, the equalizer bars and 20a, which are in the form of channels, correspondingly slant transversely of their longitudinal direction towards each other, as shown in FIG. 3, with their open sides facing downwardly.

For the pivotal attachment of the ends of the equalizer bars 20 and 20a to the brackets 22, the ends of the bars are out away to form tongue extensions 23 at the ends, as shown in FIGS. 2 and 2a, and a block 24 is snugly fitted at each end to provide a bearing for the corresponding hinge pin 21 as shown in FIGS. 2, 2a, 6, 7, 9, 11 and 13.

The equalizer bars 20 and 20a secured to the side frame brackets 22 through the hinge pins 21 as described, assist the bolster 12 in maintaining the truck side frames 10 in alignment or parallel to the respective rails. The equalizer bars 20 and 20a and the truck side frames 10 form a parallelogram, and since these are pivotally joined through the brackets 22 and the hinge pins 21, they operate as a parallel motion permitting the side frames to shift relatively endwise and into limited angular positions with respect to the equalizer bars 20 and 20a when the wheels 18 are rounding a curve. The equalizer bars 20 and 20a also serve to support the weight of the brake mechanism.

The brakes for the four car wheels 18 of each car truck are operated by four similar brake head levers of brake support arms 25, (FIGS. 1 and 2), each pivotally secured at one end to one of the equalizer bars 20 and 200 by means of a pivot or hinge pin 26, while its other end carries a brake head 27 by means of a pivot pin 28. The brake head 27 carries a faceplate 30 with a brake shoe 31 for application to a brake rotor or disc 32, which is affixed to the corresponding car wheel 18 on the inboard side thereof, to stop said disc, and which presents a brake face on its inboard side. The construction described is similar to that shown and described in the aforesaid copending application Ser. No. 417,658.

As shown in FIGS. 1, 2, 9, 10 and 14, the lower side of each equalizer bar 20 and 20a in each of the regions where a brake head lever or brake support arm 25 is pivotally connected to said equalizer bar, has welded thereto a reinforcing plate 35 and welded to said plate is a bearing 36 for a corresponding hinge pin 26.

Power for operating the brakes in each car truck is derived from two similar individual axially aligned fluid power units 40, (FIGS. 1-5, 8, l5 and 16) on opposite sides of the bolster 12. Each of these power units 40 comprises an air cylinder 41, rigidly secured to the corresponding equalizer bar 20 and 20a with its axis horizontal and in the vertical plane extending along the length of the truck and along the railway car and through the center of the bolster 12.

For supporting each cylinder 41 on the corresponding equalizer bar 20 and 20a, each of said equalizer bars is cut out to produce a recess 39 into which the lower section of the cylinder extends, and the equalizer bar is reinforced where it has been weakened by this recess by an angle iron 42 welded to the underside of the equalizer bar underneath the recess. A bracket 43 with a yoke extension 44 serving the purpose to be described, has base ears 45 secured to the outer inclined side webs 46 of the corresponding equalizer bar 20 and 20a by bolts or studs 47, and a body 48, offset upwardly into vertical position from these base ears. Each cylinder 41 is secured to the corresponding bracket 43 by means of bolts or studs 50 passing through the outer end wall 51 of the cylinder and through the body 48 of said bracket, and the yoke 44 extends horizontally from said bracket body.

Each cylinder 41 includes a piston 55, slidable therein, and connected to a peripheral. end ring 56 at one end of the cylinder by a reversely, progressively foldable skirt 59 made of rubber or other suitable resilient material, to seal the peripheral gap between the periphery of said piston and the peripheral wall of the cylinder in all positions of the piston. Air is introduced into one end of the cylinder 41 on one side of the piston 55 by means of pressure air inlet 57, and a piston rod 58, connected to said piston, extends through the wall 51 at the other end of the cylinder, so that the piston and rod serve as a power transmission means to the toggle mechanism. A spring 61 shown in the form of two coil units 62 and 63, one inside the other, bears against the piston 55 and against end wall 51, and resists the movement of the piston as it is powered by the air pressure towards said end wall. A relief valve 64 in the cylinder end wall 51 permits the air on one side of the piston 55 to escape, as the air under pressure acts on the other side of the piston.

The two inlets 57 on the two air cylinders 41 are connected to a main air pressure reservoir or chamber (not shown) of conventional type and having an outlet, which is opened when the brakes are to be applied, and which when opened delivers air to the four cylinders 41 on the two trucks carrying each railway car.

The power transmission between each cylinder 41 on each side of the bolster l2 and the two brake heads 27 on the same side of the bolster, comprises a toggle joint mechanism having two push rods 70 at an angle to each other, connected at their outer ends to the brake head levers or brake support arms 25 respectively by means of the pivot pins 28 and articulated at their inner adjoining together and to the outer end of the corresponding piston rod 58 by means of an angular swivel connector 71, pivotally connected to said rod and guided for movement along the yoke 44. This swivel connector 71 is channel-form with two similar parallel opposed web plates 73 having aligned holes 74 in the apex region of the connector and is located between two opposed arms 72 of the yoke 44 for slidable movement therealong. A bearing sleeve 75 extending between the swivel connector plates 73 and holes 74, is integral or otherwise rigidly connected to the piston rod 58. A pivot pin 76 passes through the holes 74 and through the sleeve 75 and passes with a slide fit through two aligned elongated slots 77 extending along the yoke arms 72 to guide the swivel connector 71 as well as the piston rod 58 along said yoke arms, while permitting said connector to swivel about the axis of said pin.

The swivel connector 71 has two angularly related arms 80 and the inner adjoining ends of the two pushrods 70 of the toggle joint mechanism are pivotally connected to the outer ends of said connector arms by means of pivot pins 81. The outer ends of these two pushrods 70 are pivotally connected to the outer ends of the brake head levers 25 by means of the pivot pins 28.

In the operation of the brake mechanisms shown in FIGS. 1, 2 and 3, when the brakes are not applied, these mechanisms are in the phase position shown in the drawings, with the brakeheads 27 spaced from the brake discs 32, due to the positive action of the springs 61 on said brakeheads through the pistons 55, the pushrods 70 and the brakehead levers 25 carrying said brakeheads.

Upon application of the brakes, air is admitted through the air inlets 57 into the air cylinders, by the opening of the main valve (not shown) from the main air pressure chamber (not shown). This causes the pistons 55 to be moved by braking air pressures outwardly in their cylinders away from the bolster 12 against the action of the springs 61, and this, in turn, causes the pushrods 70 to straighten out and the brakehead levers 25 to turn about the axes of their pivot pins 26 in directions to apply the brakeshoes 31 to the brake discs 32 with braking pressure.

The pivotal connections between the pushrods 70 and theswivel connectors 71, and between the swivel connectors and the piston rods 58, permit the elements of the toggle joint mechanisms to adjust themselves and to compensate automatically for uneven wear among the different brakeshoes 31, so that regardless of such uneven wear, the braking pressures applied by all of the brakeshoes in each track are substantially the same.

Upon release to atmosphere of the air braking pressure on the pistons 55, the compressed springs 61, in their releasing movements positively move the toggle joint mechanisms in a manner to move the brakeheads 27 into inoperative positions away from the brake discs 32, shown in FIGS. 1, 2 and 3.

In the conventional type of air pressure systems for applying air pressure for braking operations, the main air pressure chamber contains a definite volume of air under pressure before the initiation of the braking operation, and as the elements of the braking system are moving in braking position, the pressure in the pressure chamber falls. In the system shown herein, as the pistons 55 move in the cylinders 41 under the action of air pressure away from the bolster 12, the power air available for that purpose expands, causing thereby the force on the pistons 55 to decrease at a substantially constant rate. Fig. 17 is a graph showing this reduction in the piston force in each cylinder 41, as this piston moves through its full stroke, which in the specific form shown would be approximately 4 inches. As a result, the braking force at the end of the piston stroke in the absence of a restraining spring is not as high as it should be.

To compensate for this progressive drop in cylinder force, a toggle joint mechanism is employed to transmit power from the cylinders 41 to the brakehead levers 25. The mechanical advantage of the toggle joint mechanism increases progressively as its two pushrods 70 move towards longitudinal alignment, as shown in Fig. 18. However, as noted in the graph of Figs. 18, when such a toggle joint mechanism is used without a restraining spring, the rate of increase in mechanical advantage of this mechanism is high, at least during the terminal stages of brake application, and consequently, the braking force during these stages is applied at such excessive rates during these stages as to create undesirable shocks, impacts and concussions to the railway cars, and attachments thereto. If the toggle joint mechanism with its mechanical advantage increasing at such high rate as shown in Fig. 18, is powered by an air cylinder having decreasing power delivery characteristics, as shown in Fig. 17, this power delivery characteristic is not only compensated but is overcompensated by the toggle joint mechanism, so that the rate of delivery of braking power by the toggle joint mechanism towards the terminal brake-applying stages of its stroke is of excessive shock-producing intensity.

As a coil spring is compressed, its resistance to compression is progressively increased, and the restraining force offered by a spring to a piston operating under. the conditions here contemplated would result in a force delivered by the springpressed piston, progressively decreasing during the stroke, at a rate greater then the rate of force delivery of the piston in the absence of the restraining spring. The difference in rates of decrease in the force delivered is apparent from a comparison of Figs. 17 and 19.

If the toggle joint mechanism is powered by the cylinder 41 with the piston 55 restrained by the spring 61, the resulting braking force delivered by the toggle joint mechanism will be almost uniform through most of its stroke, and at its terminal braking stages, the rate of increase of the braking force delivered by the toggle joint mechanism would be comparatively slow, and certainly much slower than it would be in the absence of the restraining spring 61, as shown in Fig. 20. The application of the brakes therefore will not be attended with such shock and concussion.

The brake system described can be operated in conjunction with a hand brake system, as shown in Figs. 1, 2, 3, 4, 5, 9, 10, ll, 12 and 14. This hand brake system shown in conjunction with the airpowered brake system described, comprises a horizontal pull rod 90 operated from a hand-controlled device (not shown), such as a bellcrank and worm. One end of this pull rod is pivotally connected to on one end of a horizontal lever 91 on one side of the bolster 12 by means of a pivot pin 92, the other end of this lever having a rotatable bearing connection to the right-hand pivot pin 76 adjacent to the equalizer bar 20a, as shown in Figs. 1-3. The intermediate section of the lever 91 is supported for horizontal movement on a horizontal support arm 93, secured to the top web of the equalizer bar 20a. As the lever 91 is pulled by the pull rod 90 by the actuation of the hand brake system, the lever rotates about the axis of the pivot pin 76.

The angular movement of the lever 91 on one side of the bolster 12 about the corresponding pivot pin 76 is transmitted to a horizontal lever 94 on the other side of the bolster by means of a horizontal connecting link 95. This lever 94 is pivotally secured at one end by means of a pivot pin 96 to an arm 97 secured to the top web of the equalizer bar 20. The other end of this lever 94 has a rotatable bearing connection to the left-hand pivot pin 76 adjacent to the equalizer bar 20, as shown in Figs. 1-3.

The connecting link extends through the bolster l2, and has pivot pin-elongated slot connections 97 and 98 at its opposite ends to intermediate sections of the levers 91 and 94 respectively, permitting said levers to turn about the pivot axes at these connections. A pair of guides 100 secured to the equalizer bars 20 and 20a by means of brackets 101, guide the link 95 translationally endwise crosswise of the bolster 12.

In the operation of the hand brake system, when the pull rod 90 is pulled to the left (Figs. 1, 2 and 3), the lever 91 rotates clockwise about the axis of the corresponding pivot pin 76, and about the pivot axis at the connection 97, both angular movements taking place either successively or simultaneously.

These angular movements of the lever 91, cause the pivot pin 76 to move along the guide yoke 44 away from the bolster 12 and cause the pushrods 70 of the corresponding toggle joint mechanism to straighten out and to apply the brakes to the corresponding brake discs 32. At the same time or subsequent or prior thereto, the connecting link 95 is moved to the left,

causing the lever 94 to effect angular movements of this lever about the axis of its corresponding pivot pin 76 and about the pivot axis at the pivot connection 98, either in sequence or simultaneously, thereby effecting the movement of this pivot pin along the corresponding guide yoke 44 away from the bolster 12. This operation causes the pushrods 70 of the corresponding toggle joint mechanism to straighten out and to apply the brakes to the corresponding brake discs 32.

Although the different operations of the hand brake system have been described as possibly taking place in sequences, these steps, in every case, take place substantially simultaneously, so that braking forces are applied to all four of the brake discs 32 almost at the same time. i

In Figs. 21 and 22 there is illustrated a somewhat different type of cylinder and piston mechanism for operating the toggle braking linkage, it being understood that, except for the cylinder and piston mechanism, the toggle braking linkages and associated devices and their operation are otherwise the same as those previously described.

The brake-operating cylinder and piston mechanism 101 shown in Figs. 21 and 22 is secured to a cylinder support and brake rod guide 102 by bolts or studs (not shown) that pass through holes 103 in the cylinder support and into registering threaded nuts 104 fixed to the base 105 of a cylinder shell on the inner surface thereof. The shell has a cylindrical wall 106 integral with the base and a flat head 107 parallel with the base, the cylindrical wall being formed in two parts in manner hereinafter described.

A collar 108 fixed to the base 105 of the cylinder shell centrally and internally thereof, serves to guide a piston rod device 109 (whose outer end is articulated to toggle rods as in the embodiment previously described) throughout its brakeapplying stroke. The piston rod device comprises in part, a cylindrical sleeve 110 in sliding engagement with the inner cylindrical surface of the collar 108 which is recessed to present a packing ring 11 1, in contact with the piston sleeve to prevent escape of air form the cylinder, a grease well 112 for lubricating the sliding motion and a skirted washer 113 for maintaining the sliding surface of the piston sleeve clean.

The piston sleeve 110 is welded at its inner end to a flat piston head 114 of diameter somewhat smaller than the cylinder shell diameter and which has a cylindrical skirt 115 in spaced parallel relation with the cylinder wall extending from the periphery of the head 114 for a distance (about one-third the longitudinal dimension of the cylinder) backtoward the cylinder base 105. In the normal or nonbraking position of the parts, the flat piston head 114 is separated from the cylinder head by a reversely progressively foldable skirt or diaphragm 1 16 made of rubber or other suitable resilient material, to seal the gap between the outer peripheral wall of the piston and the opposed inner wall of the cylinder shell in all positions of the piston. Assembly of the cylinder and piston mechanism is facilitated by splitting the cylinder transversely perpendicular to its axis, providing the adjacent edges with outwardly extending annular lips 117 between which a thickened edge bead 118 of the foldable skirt is clamped and locking the parts together by an annular clamp 119 which tightly engages the opposite outer faces of the lips 117.

Air under pressure for operating the cylinder and piston mechanism in its brake-applying stroke is admitted through an entrance port 120 on the side of the diaphragm opposite the piston head, to move the pistonhead 114 and consequently the piston rod 109 which is articulated to the toggle rods, from the normal or solid line position shown in the drawing toward the base of the cylinder and, if the piston in its operation travels its maximum stroke, it comes to rest in the broken line position shown in the drawing wherein the cylindrical skirt 115 of the piston engages at its edge against the inner face of the cylinders base.

The piston 114 throughout its movement, is resisted by a compression spring 121 which encircles the piston rod and reacts between the base of the cylinder where the adjacent terminal coil is held in position by encircling an enlarged base portion 122 of the piston-guiding collar, and the head of the cylinder where the adjacent terminal coil is confined within a circular ring 123 welded to the cylinder head on the inner face. Note that spring 121 is of barrel shape whose coils become progressively smaller from the largest median coil toward the end coils. When the spring is compressed, its barrel shape permits the coils to nest without interference one within the other to accommodate a relatively large brake-applying piston travel or stroke for a cylinder relatively small in its longitudinal dimension.

A breather hole 124 in the bottom side only of the cylinder pennits air on one side of the cylinder to escape, as air under pressure acts on the other side of the piston.

It should be noted too, that the piston rod construction is one that compensates for any normal condition tending to exert a lateral force on the piston rod. The piston rod in the sleeve portion 110 previously referred to at the end adjacent the pistonhead, is closed for a distance approximately the depth of the piston skirt, by a solid filler piece, preferably metal, arranged always to move integrally with the sleeve. The piston rod 109 further includes a solid cylindrical rod portion 126 having diameter smaller than the internal diameter of the sleeve 110 into which the rod portion extends so as to provide clearance between the rod and the sleeve. (By way of example, for a rod having say 1 inch diameter the sleeve's internal diameter might be 1 3/16 inches. The rod 126, at its outer end, if formed with an eye 127 for pin articulation with a swivel connector such as the connector 71 described in the previous embodiment and for the same reason. The rod at its inner end has a convex spherical surface 128 of a first given radius which butts against a concave spherical surface 129 of a second somewhat greater radius presented at the end of the solid filler piece 125. An annular recess in the wall of the rod located inwardly from the convex end thereof a distance equal to said first radius accommodates an O-ring 130 of circular cross section and which, at its outer periphery is in bearing contact with the inner wall of the piston sleeve 110. With this arrangement any wear in the brakeshoes or the brake or toggle linkage that tends to displace the pivotal connection between the piston rod and the swivel connector out of the line of the piston s longitudinal travel, permits the piston rod to pivot about the center of its convex spherical end thereby substantially to confine all forces transmitted to the piston rod to those which are exerted linearly thereof.

The piston rod construction shown for transmitting force exerted on the piston to the brake shoe linkage is very simple particularly where it is desired to accommodate any lateral forces that may be exerted on the piston rod. However, the

two-piece construction of the piston rod will not insure return to normal position of the parts, i.e., where the spherical end of the rod portion 126 abuts the spherical seat of the sleeve portion 110, upon release of air pressure in the cylinder. This can readily be accomplished, however, by connecting a tension spring (not shown) at some place along the brake linkage, preferably near the parts supporting the brakeshoes so as to produce a definite bias tending to move the brakeshoes away form the brake discs when the brake applying air pressure is reduced.

It can be shown where a is the angle between the toggle rod and a horizontal line passing through the pin articulating such rod to the swivel connector, that the force exerted by the brake shoe on the brake disc can be found by the formula D=F/(2 tan a) where D the fore exerted by the brakeshoe on the brake disc; and

F the force exerted by the piston through the piston rod, i.e., the force exerted by the air on the piston head, less the compensating force exerted by the spring against the brakeapplying movement of the piston rod.

As piston travel increases, the spring, because of increased compression and in accordance with its characteristic rate, exerts an increasing retarding force to the movement of the piston so that F in the formula decreases. Likewise as piston travel increases to straighten out the toggle rods angle a and its tangent likewise decrease. Thus, by appropriately designing the geometry of the linkage and selecting an appropriate rate for the piston-retarding spring, the value D can be caused to remain substantially constant over a substantial portion of the piston travel and this whether or not the variations in piston travel result from shoe wear or other wear in the linkage.

While the improved system has been described in connection with a toggle linkage whose rods transmit force to opposed braking surfaces on opposite wheels, it is contemplated that it could also be used to transmit forces to the opposite faces of the same disc associated with a single wheel.

While the invention has been described with particular reference tospecific embodiments, it is to be understood that it is not to be limited thereto.

I claim:

1. In a railway car truck, the combination comprising a pair of coaxial car wheels, brake disc means presenting opposed braking surfaces associated with said wheels, a toggle joint mechanism comprising two rods not in alignment, articulating means connecting said rods at their inner ends to form a toggle joint, means for .guiding the rods toward alignment upon movement of said articulating means in a brake-applying direction, said toggle mechanism upon movement of said articulating means in said brake-applying direction acting to multiply a force effecting said movement with progressively increasing mechanical advantage over said brake-applying stroke, means including a fluid-pressure-operated force-transmitting means for applying a gradually decreasing force to effect movement of said articulating means in said brake-applying direction, compressible coil spring means operable to control said force-transmitting members progressively to reduce the resultant force transmitted thereby for multiplication by the progressively increasing mechanical advantage of the toggle mechanism to render the output force exerted by the toggle mechanism substantially uniform over the major portion of said brake-applying stroke, and means under control of said output forces for applying a braking effect to the opposed braking surfaces of said brake disc means.

2. In a railway car truck, the combination according to claim 1 wherein the brake disc means includes a brake disc associated with each wheel with one of said opposed braking surfaces on each disc.

3. In a railway car truck, the combination according to claim 1 wherein the fluid-pressure-operated force-transmitting means includes a cylinder containing a piston with rod connected for transmitting a brake-applying force to the toggle mechanism upon buildup of fluid pressure in the cylinder on one side of the piston therein, and wherein said compressible coil spring means surrounds said piston rod and bears one end against said piston and the other end against an end wall of the cylinder.

4. In a railway car truck, the combination according to claim 3 wherein the coils of the compression spring are nestable one within another as the piston moves on its brake applying stroke.

5. In a railway car truck, the combination according to claim 3 wherein the compressible coil spring means comprises two coiled sections arranged one within the other and exert different compressive resistance forces.

6. In a railway car truck, the combination according to claim 1, wherein the coaxial car wheels are supported on side frames, a pair of brakehead levers pivotally supported each at one end at a substantially fixed point with respect to said side frames, and means for pivotally connecting the other ends of said brakehead levers respectively to the outer ends of the rods comprising the toggle mechanism.

7. In a railway car truck, the combination according to claim 6, wherein the brakehead levers are pivotally supported on a bar extending between the side frames and connected at its ends to said side framesrespectively.

8. In a railway car truck, the combination comprising a pair of car wheels rotatable on the same axis, brake disc means presenting opposed braking surfaces associated with said wheels, a toggle joint mechanism comprising two rods articulated at their inner ends to form a toggle joint, means including fluid-pressure-operated means for transmitting a force F to effect movement of said articulating means in a brake-applying direction, said rods in normal position being disposed each at an angle a with a line parallel with the axis of the car wheels and perpendicular to the line of movement of said articulating means, means for guiding the rods toward alignment and a reduction in size of said angle 0: upon movement of said articulating means in a brake-applying direction, means operable as said rods move toward alignment to apply a force to the brake disc means associated with each wheel having the valve D in the equation D=(F/(2 tan a) and means for controlling the valve of the force F so as to render substantially uniform force D for different sizes of the angle a occurring during a major portion of the brake-applying stroke. 

1. In a railway car truck, the combination comprising a pair of coaxial car wheels, brake disc means presenting opposed braking surfaces associated with said wheels, a toggle joint mechanism comprising two rods not in alignment, articulating means connecting said rods at their inner ends to form a toggle joint, means for guiding the rods toward alignment upon movement of said articulating means in a brake-applying direction, said toggle mechanism upon movement of said articulating means in said brakeapplying direction acting to multiply a force effecting said movement with progressively increasing mechanical advantage over said brake-applying stroke, means including a fluid-pressureoperated force-transmitting means for applying a gradually decreasing force to effect movement of said articulating means in said brake-applying direction, compressible coil spring means operable to control said force-transmitting members progressively to reduce the resultant force transmitted thereby for multiplication by the progressively increasing mechanical advantage of the toggle mechanism to render the output force exerted by the toggle mechanism substantially uniform over the major portion of said brake-applying stroke, and means under control of said output forces for applying a braking effect to the opposed braking surfaces of said brake disc means.
 2. In a railway car truck, the combination according to claim 1 wherein the brake disc means includes a brake disc associated with each wheel with one of said opposed braking surfaces on each disc.
 3. In a railway car truck, the combination according to claim 1 wherein the fluid-pressure-operated force-transmitting means includes a cylinder containing a piston with rod connected for transmitting a brake-applying force to the toggle mechanism upon buildup of fluid pressure in the cylinder on one side of the piston therein, and wherein said compressible coil spring means surrounds said piston rod and bears one end against said piston and the other end against an end wall of the cylinder.
 4. In a railway car truck, the combination according to claim 3 wherein the coils of the compression spring are nestable one within another as the piston moves on its brake applying stroke.
 5. In a railway car truck, the combination according to claim 3 wherein the compressiblE coil spring means comprises two coiled sections arranged one within the other and exert different compressive resistance forces.
 6. In a railway car truck, the combination according to claim 1, wherein the coaxial car wheels are supported on side frames, a pair of brakehead levers pivotally supported each at one end at a substantially fixed point with respect to said side frames, and means for pivotally connecting the other ends of said brakehead levers respectively to the outer ends of the rods comprising the toggle mechanism.
 7. In a railway car truck, the combination according to claim 6, wherein the brakehead levers are pivotally supported on a bar extending between the side frames and connected at its ends to said side frames respectively.
 8. In a railway car truck, the combination comprising a pair of car wheels rotatable on the same axis, brake disc means presenting opposed braking surfaces associated with said wheels, a toggle joint mechanism comprising two rods articulated at their inner ends to form a toggle joint, means including fluid-pressure-operated means for transmitting a force F to effect movement of said articulating means in a brake-applying direction, said rods in normal position being disposed each at an angle Alpha with a line parallel with the axis of the car wheels and perpendicular to the line of movement of said articulating means, means for guiding the rods toward alignment and a reduction in size of said angle Alpha upon movement of said articulating means in a brake-applying direction, means operable as said rods move toward alignment to apply a force to the brake disc means associated with each wheel having the valve D in the equation D (F/(2 tan Alpha ) and means for controlling the valve of the force F so as to render substantially uniform force D for different sizes of the angle Alpha occurring during a major portion of the brake-applying stroke. 